A radiation curable resin composition capable of producing molded articles which have excellent transparency, small light-coloring resistance, high dimensional accuracy, high surface hardness, and high thermal resistance. The radiation curable resin composition for cast polymerization, comprises two different (meth)acryloyl group-containing compounds represented by general formula (1) and (2) and a radiation active initiator possessing a specific molar absorption coefficient.

A radiation curable resin composition for cast polymerization, comprising: (A) 2094.9t by weight of a (meth)acryloyl groupcontaining compound (hereinafter called "component (A)") represented by the following general formula: wherein R1 represents a hydrogen atom or a methyl group, R2 represents an alkylene group or a hydroxyalkylene group having 26 carbon atoms, R3 represents a divalent organic group, n denotes an integer from 0 to 6, m denotes an integer from 1 to 10, and L denotes an integer from 0 or 1; (B) 579.9% by weight of a (meth)acryloyl groupcontaining compound (hereinafter called "component (B)") represented by the following general formula: wherein R4 represents a hydrogen atom or a methyl group, R5 represents an alkylene group having 26 carbon atoms, and p denotes an integer from 1 to 16; and (C) 0.1 to 10% by weight of a radiation active initiator (hereinafter called "component (C)") having molar absorption coefficients of 100 Lmol~1 cm~l or more at a wave length of 360 nm and of 100 Lmol~1 cm~l or less at a wave length of 450 nm.

2.

Resin composition according to claim 1, wherein the composition has a viscosity of 10020,000 cps.

3.

Resin composition according to any one of claims 12, wherein the composition upon cure exhibits a curing shrinkage of 10% or less.

4.

A process for the production of an article by casting a radiation curable resin composition according to any one of claims 13, in a mold, and curing the resins with radiation.

5.

Product obtained by the process of claim 4, having a refractive index of 1.53 or more.

6.

Product according to claim 5 wherein the product has a modulus of elasticity in tension at 230C of 10250 kg/mm2.

7.

Product according to any one of claims 56, wherein the product has a pencil hardness of H or higher.

8.

Product according to any one of claims 57 wherein the product has a transparancy in AE of less than 3.

9.

Product according to any one of claims 58, in the form of a lens, disk, prism or lens sheet.

10.

Product according to any one of claims 58 in the form of a coating for a plastic film substrate for an optical material.

Description:

TITLE OF THE INVENTION RADIATION CURABLE RESIN COMPOSITION FOR CAST POLYMERIZATION Field of the Invention The present invention relates to a radiation curable resin composition which can be rapidly cured by radiation exposure, and, especially to a radiation curable resin composition for cast polymerization which is suitable not only for molded articles used for manufacturing optical parts such as lenses, optical disks, prisms, glass sheets, and the like, but also for surface coating materials which are applied to plastic film substrate materials used as optical materials such as substrates for liquid crystal display devices and the like.

Description of Related Art There are methods proposed for manufacturing plastic lenses or the like by irradiating a radiation curable resin composition with W-rays from a mercury lamp as activated energy rays (see Japanese Patent Applications Laid-open No. 194401/1986 and No.

207632/1989). These methods have an advantage whereby the resin composition can be cured in a short period of time by irradiation with W-rays. However, the transparency and hue of lenses produced by curing using W-ray radiation are inferior to those of polymers such as polymethyl methacrylate, polycarbonate, diethylene glycol bisaryl carbonate, or the like. Also, there is a problem of coloring by ultraviolet radiation exposure and the like after molding. In addition, in a cast molding process for a W-ray curable resin, a curing stress at the time of curing tends to remain in a molded article, which causes camber deformation and

shrinkage, leading to a reduction in dimensional accuracy.

Japanese Patent Application Laid-open No.

174910/1995 discloses a prism sheet used to improve the frontal brightness of a back light unit used in a liquid crystal display apparatus. As a method for manufacturing this prism sheet, which is a molded article molded into a specific form using a transparent material with a specific refractive index, a monobloc molding method using transparent glass with a refractive index of a specific range and a method of forming a prism-shaped article using a W-ray curable resin composition are disclosed. Furthermore, an active ray curable resin composition for cast polymerization, which is depth curable and is featured by a small optical strain in the cured product, is disclosed in Japanese Patent Application Laid-open No. 65111/1989.

Plastic materials represented by these W- ray curable resins, however, are limited in use in the fields which require a thermal resistance as described in the above Patent Application Laid-open No.

65111/1989. Specifically, such a plastic material has a fatal drawback that, when a lens sheet represented by a prism sheet obtained using the conventional W-ray curable resin is allowed to stand at a high temperature, a part of the lens sheet fuses and erodes to leave an adhesion scar on the surface of the back light, exerting an adverse influence on the optical properties.

Especially in cast polymerization, because a resin composition is polymerized by the radioactive rays transmitted from a mold made of glass or the like and from materials such as a plastic film or the like, the bulk of the rays of a short wave length is absorbed by shielding materials. The resin composition cannot

acquire sufficient energy (absorption energy) to cure itself, whereby not only the curability and productivity are reduced, but also unreacted substances remain in the cured product, resulting in reductions in surface hardness and thermal resistance, which are fatal problems.

Problems to be Solved by the Invention The present invention has been undertaken to solve the above conventional problems and has an object to provide a radiation curable resin composition which has excellent transparency, small light-coloring resistance, high dimensional accuracy, excellent curability, high surface hardness, and high thermal resistance so that it can produce at high yield molded articles, which never stick to or erode an adjacent substrate or the like in a high temperature condition.

Means for the Solution of the Problems The present inventors have conducted earnest studies in view of this situation, and, as a result, discovered the following radiation curable resin composition to complete the present invention.

Accordingly, the present invention provides a radiation curable resin composition for cast polymerization, comprising: (A) 20-94.9% by weight of a (meth)acryloyl group-containing compound (hereinafter called "component (A)") represented by the following general formula (1): wherein R1 represents a hydrogen atom or a methyl group, R2 represents an alkylene group or a hydroxyalkylene

group having 2-6 carbon atoms, R3 represents a divalent organic group, n denotes an integer from 0 to 6, m denotes an integer from 1 to 10, and L denotes an integer from 0 or 1; (B) 5-79.9% by weight of a (meth)acryloyl group-containing compound (hereinafter called "component (B)") represented by the following general formula (2): wherein R4 represents a hydrogen atom or a methyl group, R5 represents an alkylene group having 2-6 carbon atoms, and p denotes an integer from 1 to 16; and (C) 0.1 to 10% by weight of a radiation active initiator (hereinafter called "component (C)") having molar absorption coefficients of 100 L-mol~1-cm~ or more at a wave length of 360 nm and of 100 Lmol1 cm1 or less at a wave length of 450 nm.

The present invention will now be explained in detail by way of an embodiment.

In (meth)acryloyl group-containing compounds used as component (A) of the present invention, as the alkylene group or the hydroxyalkylene group having 2-6 carbon atoms, which is represented by R2 in the above formula (1), divalent organic groups represented by the following formulae (3-1) to (3-11) are exemplified: -CH2CH2- (3-1) -CH2CH2CH2- (3-2)

Among these, the organic groups represented by formulae (3-1), (3-3), and (3-11) are preferred.

In addition, as preferable organic groups represented by R3 when L is 1 in the above general formula (1), organic groups represented by the following formulae (4-1) to (4-7) are exemplified:

Among these, the organic groups represented by formula (4-1) are particularly preferable. Also, compounds having a structural formula in which hydrogens of optional aromatic rings in general formula (1) are substituted with a bromine atom and a chlorine atom may be used.

The proportion of component (A) in the composition is generally from 20 to 94.9% by weight and preferably from 30 to 70% by weight. When the proportion of component (A) is within the above defined range, the cured product has an appropriate refractive index and exhibits excellent surface hardness. If the proportion is less than 20% by weight, only cured products having a reduced refractive index and a poor surface hardness are obtained. On the other hand, if the proportion exceeds 94.9% by weight, only cured products which greatly shrink in the curing process and have a lower dimensional accuracy are obtained.

In (meth) acryloyl group-containing compounds used as the component (B) of the present invention, as the alkylene group having 2-6 carbon atoms, which is represented by R5 in the above formula (2), divalent organic groups represented by the following formulae (5-1) to (5-10) are exemplified: -CH2CH2- (5-1) -CH2CH2CH2- (5-2)

Among these, the organic groups represented by formulae (5-1), (5-3), and (5-10) are preferred.

The proportion of the component (B) in the composition is generally from 5 to 79.9% by weight and preferably from 10 to 40% by weight. When the proportion is within the above defined range, a cured product, which has an appropriate hardness and is superior in dimensional accuracy, long-term durability, and thermal resistance, can be obtained. If the proportion is less than 5% by weight, the hardness of the cured product decreases to cause the cured product to adhere to a substrate, whereas if the proportion exceeds 79.9% by weight, only a cured product which shrinks greatly at the time of curing and is inferior in dimensional accuracy is obtained.

The composition of the present invention may include a copolymerizable monomer (hereinafter called "component (X)") other than the components (A) and (B). This copolymerizable monomer may be either a monofunctional monomer or a polyfunctional monomer.

wherein R6 represents a hydrogen atom and a methyl group, R7 represents an alkylene group having 2-6, preferably 2-4, carbon atoms, R8 represents a hydrogen atom or an alkyl group having 1-12, preferably 1-9, carbon atoms, R9 represents an alkylene group having 2- 8, preferably 2-5, carbon atoms, R10 represents a hydrogen atom or a methyl group, q denotes an integer from 0 to 12, and preferably from 1 to 8, r denotes an integer from 1 to 8, and preferably from 1 to 4, and s denotes an integer from 1 to 8 and preferably from 1 to 4.

Given as examples of the polyfunctional monomer are monomers containing a plurality of (meth)acryloyl groups such as dicyclopentenyl di(meth)acrylate, tricyclodecanediyldimethylene di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra (meth) acrylate, polyester di(meth)acrylate, and the like. Among these compounds, tricyclodecanediyldimethylene di (meth) acrylate is desirable.

As commercially available compounds of the polyfunctional monomer used as the component (X), for example, Yupimer W, SA1002 (manufactured by Mitsubishi Chemical Corp.), KAYARAD R-604, DPCA-60, DPCA-30, DPCA- 120, HX-620, D-310, D-330 (manufactured by Nippon Kayaku Co., Ltd.), Aronix M-215 (manufactured by Toagosei Co., Ltd.), or the like can be used.

The copolymers of the component (X) may be used either singly or in combinations of two or more.

The proportion of the component (X) in the composition is from 0 to 60% by weight and preferably from 0 to 40% by weight.

The radiation active initiator used as the component (C) of the present invention is characterized in that the molar absorption coefficient is 100 L-mol~1 cm~l or more at a wave length of 360 nm and 100 L-mol~1 cm~l or less at a wave length of 450 nm.

Here, the above molar absorption coefficient is defined as one which is calculated according to the following formula, for which the absorbance of a methanol solution containing 0.5 to 3 mmol/L of the target compound is measured at 250C using an absorptiometer: Molar absorption coefficient (L-mol~1-cm~l) = Absorbance/(Solution density (mol.L1) Optical path (cm)) The molar absorption coefficient of the component (C) is as high as 100 L-mol~1-cm~l or more even at a wave length of 360 nm which is out of the range of the wave length absorbed by the mold and substrate materials used in cast polymerization. The resin composition, therefore, can absorb sufficient energy to polymerize, whereby unreacted substances in the resulting cured product decrease, hence molded articles possessing excellent thermal resistance can be produced.

If the molar absorption coefficient of the radiation active initiator at a wave length of 360 nm is not higher than 100 L-mol~1-cm~l, the resin composition cannot acquire sufficient energy to polymerize. On the other hand, if the molar absorption coefficient of the radiation active initiator at a wave length of 450 nm exceeds 100 L-mol~1 cm~l, the coloring of the resulting cured product increases, causing optical properties to be damaged, especially when optical products are molded.

2-dimethylamino-l- (4-morpholinophenyl)butan-l-one, 3- methylacetophenone, and 3,3',4,4'-tetra(t-butyl peroxycarbonyl) benzophenone (BTTB), and further combinations of BTTB and a coloring substance photosensitizer such as xanthene, thioxanthene, cumarin, ketocumarin or the like. Moreover, the compounds which are represented by the following formula (9) can be used. wherein Rills independently represent an alkyl group having 1-5 and preferably 1-3 carbon atoms and t denotes an integer from 2 to 50 and preferably from 2 to 20.

Among these compounds, 2-hydroxy-2-methyl- l-phenylpropan-l-one and l-hydroxycyclohexyl phenyl ketone are desirably used.

Examples of commercially available products of these radiation active initiators include Darocure 1173 (manufactured by Merck Co.) and Irgacure 184 (manufactured by Ciba-Geigy).

The proportion of the radiation active initiator, which is the component (C), is generally from 0.1 to 10% by weight and preferably from 0.1 to 5% by weight of the total amount of the composition. The proportion exceeding 10% by weight sometimes has an adverse effect on the storage stability of the composition and the properties and appearance of the cured product. On the other hand, if the proportion is not more than 0.1% by weight, there is the case where the curing rate decreases.

The radiation curable resin composition can be prepared by mixing the aforementioned components according to a general method. The viscosity of the composition of the present invention prepared in this manner is generally from 100 to 20,000 cps, preferably from 500 to 10,000 cps, at 250C.

The radiation curable resin composition of

the present invention is cured to produce a cured product with the modulus of elasticity in tension at 230C being 10-250 kg/mm2. Also, the refractive index nD25 (refractive index of sodium D rays at 250C) of the cured product is 1.53 or more and preferably 1.55 or more. Moreover the curing shrinkage rate associated with curing is 10% or less, preferably 8% or less, and more preferably 6% or less. Preferably, the product has a pencil hardness of H or higher. Incidentally, the radiation in the present invention includes ultraviolet radiation, visible rays, infrared radiation, rays, p- rays, y-rays, and X-rays.

EXAMPLES The present invention will be explained in more detail by way of examples, which are not intended to be limiting of the present invention.

Examples 1-3 and Comparative Examples 1-3 The components of each of the compositions shown in Table 1 were placed in a reaction vessel equipped with a stirrer and stirred for three hours while controlling the temperature at 50 to 60"C. Using these resin compositions which were uniformly stirred in this manner, the properties were measured. Each value for Examples 1-3 and Comparative Examples 1-3 in Table 1 is expressed as that of a percent by weight.

Test Example A test specimen was made by the following procedures using each of the resulting resin compositions prepared in the aforementioned Examples and Comparative Examples to evaluate the refractive index, pencil hardness, curing shrinkage rate, and substrate erosion over a long-term under high temperature storage. The results are shown in Table 2.

Production of test specimens: Resin composition at a thickness of about 200 pm was applied to the surface of a glass plate using a 15 mil applicator bar and was irradiated with W-rays at a dose of 1.0 J/cm2 in air to obtain a cured film. The cured film was then peeled away from the glass plate and kept at 230C under a relative humidity of 50% for 24 hours to prepare a test specimen.

Refractive index: The refractive index of the test specimen at 250C was measured using an Abbe refractometer.

Hardness: The pencil hardness of the test specimen of the above resin composition was measured using a pencil scratch test machine under a load of 1 kg according to JIS K5400.

Curing shrinkage rate: Resin composition at a thickness of about 100 pm was applied to the surface of a film of PET (polyethylene terephthalate) with a thickness of 120 pm using a 250 pm thickness applicator bar and was irradiated with W-rays at a dose of 1.0 J/cm2 in air.

Four pieces which were each 10 by 10 cm were cut off the four corners of the test specimen and the warp rates of the four pieces were measured using a slide caliper and averaged. The curing shrinkage rate was evaluated by rating the average warp rate as "O", "A", and "X" when the average warp rate was not more than 10 mm, more than 10 mm and not more than 15 mm, and 15 mm or more respectively.

Transparency: Resin composition at a thickness of about 100 mm was applied to the surface of a slide glass using a 250 mm thickness applicator bar and was irradiated with W-rays at a dose of 1.0 J/cm2 in air to obtain a cured film. The color difference (hE) of the test piece on which the cured film was formed was measured by a color-difference meter (SZ-z80/MSP, manufactured by Nippon Denshoku Co., Ltd.) using a slide glass on a standard white plate as a reference.

The transparency was evaluated by rating the color difference (hE) as "O", "A", and "X" when the color difference (hE) was not more than 3, more than 3 and not more than 5, and 5 or more respectively.

Substrate erosion: Resin composition was injected into a prism sheet mold having micro-irregularity. A transparent PET sheet with a thickness of 125 m was allowed to adhere to the resin composition. Then W-rays were applied to the side of the PET sheet at a dose of 1.0 J/cm2 to prepare a cured film. The cured film was cut into strip specimens of 5 mm width and 50 mm length. Five strip specimens were arranged on a glass plate at intervals of 5 mm. An acryl plate with a thickness of 2 mm was

placed on the strip specimens and the circumference of the acryl plate was sealed with adhesive tape in the condition that a load of 20 g/cm2 was applied to the acryl plate. This glass plate was kept in a thermostat at 1000C for one hour and then removed. The load and the acryl plate on the glass plate were released to observe the portion of the acryl plate, which contacted the strip specimens, and thereby to confirm whether there were adhesive traces or not. The substrate erosion was evaluated by rating the observed results as "0" and "X" when the adhesive traces were unobserved and observed respectively.

exhibited a large curing shrinkage rate and increased substrate erosion. In addition, the composition of Comparative Example 2 excluding component (A) contained in the composition of the present invention, exhibited a slightly larger curing shrinkage rate. Also, substrate erosion was found in Comparative Example 2.

Substrate erosion was also found in the composition of Comparative Example 3.

As is clear from the above explanations, the radiation curable resin composition of the present invention has excellent features in that it has excellent transparency, small light-coloring resistance, extremely small curing shrinkage in the curing step, superior curability, high surface hardness, and high thermal resistance, hence it can produce at high yield molded articles which have high dimensional accuracy and never adhere to or erode an adjacent substrate or the like at high temperatures.

The composition of the present invention is, therefore, suitable for producing optical parts such as a lens, optical disk, prism, lens sheet, and the like. Also, it is suitable for use as a surface coating material for a plastic film substrate material used for an optical material such as a substrate for a liquid crystal display device. Also, it can be used as a coating material for wood, paper, plastics, metals, ceramics, and the like.